1. Field of the Invention
The present invention relates to a method for producing a mold for use in duplicating a light diffusion sheet, a light diffusion sheet and a method for producing the same, and a screen.
2. Description of the Related Art
In recent years, as means of presenting materials in a meeting and the like, over head projectors and slide projectors are widely used. Further, video projectors and moving picture film projectors using liquid crystal for home use are being spread. A projection method in these projectors is such that light emitted from a light source is modulated by, for example, a transmissive liquid-crystal panel to form image light, and the image light is projected on a screen through optics, such as a lens.
For example, a projector apparatus, which can form a color image on a screen, includes a lighting optical system which splits a ray of light emitted from a light source into rays of red (R) light, green (G) light, and blue (B) light and converges the individual rays of light to predetermined optical paths, a liquid-crystal panel (light valve) which modulates individually the light fluxes of RGB colors split by the lighting optical system, and a light combining part which combines the light fluxes of RGB colors modulated by the liquid-crystal panel, and the color image combined by the light combining part is magnified by means of a projection lens and projected on a screen.
Further, recently, there has been developed a projector apparatus of a type spatially modulating the light fluxes of RGB colors using a narrow-band three primary-color light source as a light source and using a grating light valve (GLV) instead of the liquid-crystal panel.
In the above-mentioned projector apparatuses, a screen for projector is used for viewing the projected image. The screen for projector is roughly classified into a screen for front projector such that image light is projected from the front side of the screen to see the reflected light of the projected light by the screen, and a screen for rear projector such that image light is projected from the back side of the screen to see the transmitted light through the screen from the front side of the screen. The screens of any types are required to have excellent recognizability and a large viewing angle.
For this reason, in the screens of any types, typically, a light diffusion sheet for scattering light is formed on the surface of the screen, and the light diffusion sheet makes image light be uniformly diffused and emitted from the entire effective region of the screen.
As a method for producing a light diffusion sheet, there have been a method in which a speckle pattern, which is caused when a roughened surface is illuminated a coherent light flux, is formed in a photosensitive resin to produce a light diffusion sheet (see, for example, Japanese Patent Application Publications S53-51755 and 2001-100621), a method in which a mask is prepared and burned on a photosensitive resin to produce a light diffusion sheet, and a method in which the surface of a mold base material, such as a metal or a resin, is directly ground by mechanical processing to prepare a mold having a finely uneven surface formed, and the surface form of the mold is transferred to an ultraviolet curing resin or the like to produce a light diffusion sheet.
In addition, there have been a method in which a composition including resin particles dispersed in a resin binder is applied to a transparent substrate to produce a light diffusion sheet, and a method in which a mold having an uneven surface is prepared by subjecting a mold base material to sandblasting, and the surface form of the mold is transferred to an ultraviolet curing resin or the like to produce a light diffusion sheet (see, for example, Japanese Patent Application Publication 2000-284106).
By the way, the light diffusion sheet is frequently required to have properties such that the light diffused by the light diffusion sheet is directed to a desired range, namely, the diffusion angle in the longitudinal direction is different from the diffusion angle in the lateral direction. In the production of the light diffusion sheet, a method in which a speckle interference or mask pattern is transferred to a photosensitive resin has been employed.